[CT414]: Add Assignment 2 code
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Map;
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import java.io.IOException;
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import java.io.File;
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import java.io.FileReader;
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import java.io.BufferedReader;
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import java.util.Scanner;
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public class MapReduceFiles {
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public static void main(String[] args) {
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if (args.length < 3) {
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System.err.println("usage: java MapReduceFiles file1.txt file2.txt file3.txt");
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}
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Map<String, String> input = new HashMap<String, String>();
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try {
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input.put(args[0], readFile(args[0]));
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input.put(args[1], readFile(args[1]));
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input.put(args[2], readFile(args[2]));
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}
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catch (IOException ex)
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{
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System.err.println("Error reading files...\n" + ex.getMessage());
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ex.printStackTrace();
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System.exit(0);
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}
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// APPROACH #1: Brute force
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{
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Map<String, Map<String, Integer>> output = new HashMap<String, Map<String, Integer>>();
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Iterator<Map.Entry<String, String>> inputIter = input.entrySet().iterator();
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while(inputIter.hasNext()) {
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Map.Entry<String, String> entry = inputIter.next();
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String file = entry.getKey();
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String contents = entry.getValue();
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String[] words = contents.trim().split("\\s+");
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for(String word : words) {
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Map<String, Integer> files = output.get(word);
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if (files == null) {
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files = new HashMap<String, Integer>();
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output.put(word, files);
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}
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Integer occurrences = files.remove(file);
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if (occurrences == null) {
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files.put(file, 1);
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} else {
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files.put(file, occurrences.intValue() + 1);
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}
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}
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}
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// show me:
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System.out.println(output);
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}
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// APPROACH #2: MapReduce
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{
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Map<String, Map<String, Integer>> output = new HashMap<String, Map<String, Integer>>();
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// MAP:
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List<MappedItem> mappedItems = new LinkedList<MappedItem>();
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Iterator<Map.Entry<String, String>> inputIter = input.entrySet().iterator();
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while(inputIter.hasNext()) {
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Map.Entry<String, String> entry = inputIter.next();
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String file = entry.getKey();
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String contents = entry.getValue();
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map(file, contents, mappedItems);
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}
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// GROUP:
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Map<String, List<String>> groupedItems = new HashMap<String, List<String>>();
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Iterator<MappedItem> mappedIter = mappedItems.iterator();
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while(mappedIter.hasNext()) {
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MappedItem item = mappedIter.next();
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String word = item.getWord();
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String file = item.getFile();
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List<String> list = groupedItems.get(word);
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if (list == null) {
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list = new LinkedList<String>();
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groupedItems.put(word, list);
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}
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list.add(file);
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}
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// REDUCE:
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Iterator<Map.Entry<String, List<String>>> groupedIter = groupedItems.entrySet().iterator();
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while(groupedIter.hasNext()) {
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Map.Entry<String, List<String>> entry = groupedIter.next();
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String word = entry.getKey();
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List<String> list = entry.getValue();
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reduce(word, list, output);
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}
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System.out.println(output);
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}
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// APPROACH #3: Distributed MapReduce
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{
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final Map<String, Map<String, Integer>> output = new HashMap<String, Map<String, Integer>>();
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// MAP:
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final List<MappedItem> mappedItems = new LinkedList<MappedItem>();
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final MapCallback<String, MappedItem> mapCallback = new MapCallback<String, MappedItem>() {
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@Override
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public synchronized void mapDone(String file, List<MappedItem> results) {
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mappedItems.addAll(results);
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}
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};
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List<Thread> mapCluster = new ArrayList<Thread>(input.size());
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Iterator<Map.Entry<String, String>> inputIter = input.entrySet().iterator();
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while(inputIter.hasNext()) {
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Map.Entry<String, String> entry = inputIter.next();
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final String file = entry.getKey();
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final String contents = entry.getValue();
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Thread t = new Thread(new Runnable() {
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@Override
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public void run() {
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map(file, contents, mapCallback);
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}
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});
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mapCluster.add(t);
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t.start();
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}
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// wait for mapping phase to be over:
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for(Thread t : mapCluster) {
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try {
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t.join();
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} catch(InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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// GROUP:
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Map<String, List<String>> groupedItems = new HashMap<String, List<String>>();
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Iterator<MappedItem> mappedIter = mappedItems.iterator();
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while(mappedIter.hasNext()) {
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MappedItem item = mappedIter.next();
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String word = item.getWord();
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String file = item.getFile();
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List<String> list = groupedItems.get(word);
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if (list == null) {
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list = new LinkedList<String>();
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groupedItems.put(word, list);
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}
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list.add(file);
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}
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// REDUCE:
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final ReduceCallback<String, String, Integer> reduceCallback = new ReduceCallback<String, String, Integer>() {
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@Override
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public synchronized void reduceDone(String k, Map<String, Integer> v) {
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output.put(k, v);
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}
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};
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List<Thread> reduceCluster = new ArrayList<Thread>(groupedItems.size());
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Iterator<Map.Entry<String, List<String>>> groupedIter = groupedItems.entrySet().iterator();
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while(groupedIter.hasNext()) {
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Map.Entry<String, List<String>> entry = groupedIter.next();
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final String word = entry.getKey();
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final List<String> list = entry.getValue();
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Thread t = new Thread(new Runnable() {
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@Override
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public void run() {
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reduce(word, list, reduceCallback);
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}
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});
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reduceCluster.add(t);
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t.start();
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}
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// wait for reducing phase to be over:
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for(Thread t : reduceCluster) {
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try {
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t.join();
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} catch(InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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System.out.println(output);
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}
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}
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public static void map(String file, String contents, List<MappedItem> mappedItems) {
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String[] words = contents.trim().split("\\s+");
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for(String word: words) {
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mappedItems.add(new MappedItem(word, file));
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}
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}
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public static void reduce(String word, List<String> list, Map<String, Map<String, Integer>> output) {
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Map<String, Integer> reducedList = new HashMap<String, Integer>();
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for(String file: list) {
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Integer occurrences = reducedList.get(file);
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if (occurrences == null) {
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reducedList.put(file, 1);
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} else {
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reducedList.put(file, occurrences.intValue() + 1);
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}
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}
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output.put(word, reducedList);
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}
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public static interface MapCallback<E, V> {
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public void mapDone(E key, List<V> values);
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}
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public static void map(String file, String contents, MapCallback<String, MappedItem> callback) {
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String[] words = contents.trim().split("\\s+");
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List<MappedItem> results = new ArrayList<MappedItem>(words.length);
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for(String word: words) {
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results.add(new MappedItem(word, file));
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}
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callback.mapDone(file, results);
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}
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public static interface ReduceCallback<E, K, V> {
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public void reduceDone(E e, Map<K,V> results);
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}
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public static void reduce(String word, List<String> list, ReduceCallback<String, String, Integer> callback) {
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Map<String, Integer> reducedList = new HashMap<String, Integer>();
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for(String file: list) {
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Integer occurrences = reducedList.get(file);
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if (occurrences == null) {
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reducedList.put(file, 1);
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} else {
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reducedList.put(file, occurrences.intValue() + 1);
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}
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}
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callback.reduceDone(word, reducedList);
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}
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private static class MappedItem {
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private final String word;
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private final String file;
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public MappedItem(String word, String file) {
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this.word = word;
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this.file = file;
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}
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public String getWord() {
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return word;
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}
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public String getFile() {
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return file;
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}
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@Override
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public String toString() {
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return "[\"" + word + "\",\"" + file + "\"]";
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}
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}
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private static String readFile(String pathname) throws IOException {
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File file = new File(pathname);
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StringBuilder fileContents = new StringBuilder((int) file.length());
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Scanner scanner = new Scanner(new BufferedReader(new FileReader(file)));
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String lineSeparator = System.getProperty("line.separator");
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try {
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if (scanner.hasNextLine()) {
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fileContents.append(scanner.nextLine());
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}
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while (scanner.hasNextLine()) {
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fileContents.append(lineSeparator + scanner.nextLine());
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}
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return fileContents.toString();
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} finally {
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scanner.close();
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}
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}
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}
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